Expandable structure



FIG. 1 is a perspective view of an embodiment of an expandable structure showing my new design.

FIG. 2 is an enlarged perspective view of a front upper corner of the expandable structure of FIG. 1.

FIG. 3 is a perspective view of an embodiment of an expandable structure showing my new design; and,

FIG. 4 is a perspective view of an embodiment of an expandable structure showing my new design.

Background features are shown in broken lines for illustrative purposes only and form no part of the claimed design. 

CLAIM The ornamental design for an expandable structure, as shown and described. 